1. Field of the Invention
The present invention relates to the field of cargo handling, and in particular, to the rapid depalletizing and loading of cartons of frozen animal products onto a refrigerated vessel.
2. Background of the Invention
While there have been significant advances in the methods employed for the loading and unloading of vessels, the loading of refrigerated, cartonized cargo, and in particular, frozen animal products has proved particularly difficult due to several intractable problems. As a result, the transfer of the products from the packers to their loading aboard a vessel is presently carried out by processes that involve high costs and significant expenditure of manual labor, and which include bottlenecks that slow the process, that may result in product degradation or spoilage, and that result in long loading times for the product onto the vessel. It is presently common for the handling of cartons of frozen animal products to proceed as follows.
A large volume of animal products such as frozen chicken, turkey, beef, pork and seafood products (including livers, hearts, other parts, deboned meat and the like) are frozen and shipped within and exported from the U.S. in relatively shallow, rectangular boxes. For example, chicken thighs, legs or quarters may be shipped in cartons of about 23.5 inches in length by 16.5 inches in width by 4 to 6.25 inches in height (59.7 cm by 41.9 cm by 10.2 to 15.9 cm). A preferred standardized box size for use with the present invention would be 24 inches by 16 inches (61.0 cm by 40.6 cm) with the height of the box varied to hold the particular products to be shipped. A box of such dimensions containing frozen chicken parts may weigh on the order of 30 to 45 pounds (14 to 20 kg).
As the cartons are generally filled fairly completely with unfrozen animal products, and the animal products are subsequently frozen while in the carton, the cartons of frozen animal products tend to be comparatively resistant to compressive forces. The cartons may also be slightly distorted from their rectangular shape owing to volume changes accompanying freezing and to their handling and stacking. For simplicity, reference will hereafter be made to cartons of frozen chicken, as other animal products may be handled in a similar manner.
Owing to the size restrictions imposed by standard trucks and trailers, the cartons are normally stacked on 40×48 inch (102×122 cm) pallets in layers of five cartons arranged with two cartons placed on the pallet in an end-to-end relationship beside three cartons placed side to side with their long axes perpendicular to those of the first two cartons. While the exact size of the stack of cartons may vary depending on the exact dimensions of the cartons, stacks of cartons and layers of such stacks will be referred to herein as having the foregoing dimensions or having a wider side of 48 inches (122 cm) and a narrower side of 40 inches (102 cm). These dimensions are, however, approximate, and may vary not only depending on the box dimensions, but also from such factors as bulging of the cartons of frozen chicken and irregularities in the stacking pattern. In general, however, the cartons have a relatively low aspect ratio (length divided by height). For example, a 4″ tall by 16″ long carton would have an aspect ratio of 0.25. This is significantly lower than, for example, the common apple boxes.
A palletload of cartons generally contains between about 10 to 12 such layers of cartons. A palletload of cartons arranged in this manner would have five cartons per layer. A 12 layer stack of cartons weighing 30 pounds (14 kg) would thus weigh about 1800 pounds (818 kg). Three such stacks of cartons would thus weigh about 5400 pounds (2454 kg, equal to 2.454 metric tons).
Although it is the general practice to use pallets having dimensions of 40×48 inches (102×122 cm) in the frozen animal products industry, which facilitate loading thereof into enclosed vans or trailers, 48×48 inch pallets (122×122 cm), which hold six rather than five cartons per layer, are sometimes used. In such case, the cartons are generally arranged in layers, each such layer having two rows of three cartons with the three cartons of each row in side-to-side arrangement.
The stacking pattern for either the 48×48 or 40×48 inch pallets (122×122 cm or 102×122 cm) may be varied, as by rotating it from layer to layer. For the 40×48 inches (102×122 cm) pallets, for example, the two end-to-end cartons may be arranged along one of the long edges of the pallet in one layer and along the other long edge in the next layer.
Presently, wooden pallets are typically made of three parallel beams arranged with a center beam and two outer beams on either side thereof. Boards or other such support members are nailed, stapled or otherwise fastened to the upper and lower surfaces of the beams transversely to the beams to form the upper and lower surfaces of the pallet. Lift channels extending parallel to the beams are thus formed between the upper and lower transversely-mounted boards. Apertures may be provided in the beams along their lower edges and/or boards may be removed from the lower pallet surface in the area of the apertures to permit insertion of lift truck blades into the pallet transversely to the beams and lift channels (these are often called “4-way” pallets, as a lift truck can insert the lift blades into the pallet from any of four directions).
The packer sends the fresh chicken parts in such palletloads to a blast freezer/cold storage warehouse. At the warehouse, the cartons are restacked with spacers between the layers thereof. The spacers allow the circulation of air between the layers of cartons. Once the cartons are so stacked, the palletload of cartons are transferred to a blast freezer, which forces air chilled to about −40° F. (−40° C.) between and around the cartons. The chicken parts should be cooled in the blast freezer to 0° F. (−17.7° C.) and should be held at that temperature. When the freezing process is completed, the cartons are removed from the blast freezer and placed in a rotator. The load of cartons is then rotated 90 degrees onto its side, the spacers are removed, and the load of cartons is then rotated back to an upright position in which it rests once more on the pallet. In order to facilitate transportation and storage of the stacks of cartons, the stacks may be, and typically are, wrapped with a stretchable plastic film to help reduce sliding of the layers of cartons relative to one another. Lift trucks are then used to move the cartons of frozen chicken products and transport them into the cold storage warehouse.
When the time comes to load a ship, lift trucks are used to remove the palletloads of stacks of cartons of chicken parts from the warehouse, and place them inside dry van trucks or truck trailers for transportation to the dock. The trucks or truck trailers are typically uninsulated and unrefrigerated, and thus can provide a deleterious environment to the frozen product contained therein if they are not soon loaded into a refrigerated ship. At the dock, the cartons are removed from the truck trailer by lift trucks and placed on the dock. Alternatively, if the cold storage warehouse is sufficiently near to the dock, the lift trucks may transport the palletloads of stacks of cartons directly to the dock. In either case, the palletloads of stacks of cartons are subsequently lifted into the hold using the ship's gear, such as by using slings, lifting platforms, lift cages, flying forks or the like to lift the cartons and pallets.
Many of the ships transporting cartons of frozen chicken internationally are older vessels having ship's gear with a three-ton (metric) rated capacity. This permits them to lift up to three stacks of cartons at a time, depending on the weight of the stacks and of the gear used to lift them. However, other ships may have cranes with capacities of five or more tons. The mass of lift cages, of course, can be substantial, approaching one ton for a lift cage that can be used to lift two stacks of cartons. Thus, with three-ton ship's gear, it would generally only be possible to lift two stacks of cartons into the hold of the vessel at a time.
In the hold, lift trucks engage the pallets and transport the pallets with their stacks of cartons to locations near where the cartons will be stowed. Stevedores then manually remove the cartons from the pallets and stack the cartons without pallets for shipping. The pallets are then returned to the square of the hatch and are stacked to be hoisted out of the hold and back onto the dock by the ship's gear. The square of the hatch is the volume of space extending vertically downward from the open hatch to the floor of the cargo hold.
This process is quite inefficient. Delays in bringing a sufficient quantity of product to the dock and in unloading the cartons from the truck can increase the time needed to load the vessel. The space constraints in the vessel limit the number of workers who can be engaged in stowing of the cartons, and thus may create a backup for product arriving at the dock. Excessive delays in loading which result in the cartons being left on the dock or in the truck can allow the product to begin to thaw, which can result in spoilage or otherwise render the product unmarketable. Delay in loading may also result in increased condensation of moisture on the cartons which can complicate the handling process. As the industry is seeking to use less wax on the cartons and to utilize paper-coated boxes, the damaging effect of condensation and internal thawing on the boxes is increased.
The breakage rate for pallets during this process is fairly high. As many as half of the pallets suffer some breakage, and this can result in splintered wood, which may contain protruding nails, being left at the warehouse, on the dock and in the cargo hold of the vessel. Additional work is thus required to collect the pallets and pallet debris, to extract it from the hold of the ship or remove it from the dock, and to repair or discard the broken pallets. Further, the existence of pallet debris at the warehouse, on the dock, and in particular in the hold of the vessel, presents a risk of injury to workers.
Inefficient as this method of handling may be, there are a number of constraints that have made it difficult to improve. The main problem encountered is that the holds of the ship are irregular both in the overhead clearance and in the shape of the floor space. Not only does the overhead clearance of the cargo holds vary from ship to ship, and perhaps within a ship from hold to hold, the internal structure of the vessel and of the cooling system within it can result in overhead clearances that vary depending on the location within the hold.
Another difficulty in loading such cargoes is that the cartons are typically stacked to a uniform height after blast freezing. This is necessary for efficient use of the cold storage warehouse. This uniform height is generally ten or twelve layers of boxes arranged on a lift truck pallet, but it may vary somewhat from this number depending on the size of the cartons. The cartons are unitized by wrapping them with a stretchable plastic film that aids in transportation of the palletloads by lift truck, etc. However, space on refrigerated vessels is at such a premium that the wasted space of such pallets is considered undesirable. Thus, it has been considered necessary to avoid stowing the cartons on the pallets, and thus the practice of manually stowing the cartons in the ship by restacking them without the pallets has persisted. Moreover, since the ceiling height of holds on ships varies, and is seldom equal to the height of the cartons when stacked for warehousing purposes, it has heretofore been considered essential to manually stack the cartons in order to obtain as complete a filling of the vessel as possible.
Load push lift trucks have been used to push cargo off the lift truck blades. A load push lift truck has at least two blades extending from its lift mechanism. Typically, the blades are relatively broad, and may have relatively smooth or polished upper surfaces to facilitate the sliding of the cartons thereon. A push plate associated with the lift mechanism can be extended by means of hydraulic cylinders from a retracted position adjacent the lift mechanism to a position adjacent the ends of the blades. If the stack of cartons is resting on the blades of the lift truck, the push mechanism may also be used to push the cartons off the blades and/or to extract the blades from under cargo as the lift truck moves backward away from the desired position of the stack of cartons. Such a lift truck may include a side-shift mechanism which permits small lateral adjustments in the position of the cargo to facilitate its precise placement. Such load-push lift trucks are known in the art of specialized lift trucks.